Electric-field gradients in the yttrium deuterides YD2.25 and YD3

摘要

The electric-held gradients (EFG) were calculated by density-functional methods for the deuterium sites in ordered YD3 and hypothetical YD2.25. For the latter, five different structure models were considered. Two of them belong to the space group Pm (3) over bar m (no. 221) and three others to space group I4/mmm (no. 139). The calculations were made for both ideal and off-center atom positions which were found by total energy and force minimizations. The largest component of the EFG tensor after transformation to principle axes, IV,II. is obtained for the tetrahedral sites and the structures with the off-center displacements of deuterium atoms. For two structure models the obtained values for V-zz an very close to the one for the H-2 low temperature NMR spectrum component in YD2+x. The calculations for hexagonal YD3 with space group P (3) over bar c 1 (no. 165) showed three distinct values for V-zz corresponding to the tetrahedral site D(T) and the octahedral sites D(m1) and D(m2). Although they are of the same order of magnitude as those seen in the high-temperature H-2 NMR YD3 spectrum the agreement is not satisfactory. Further investigations of the structure of YD3 are suggested. [References: 31]